This invention relates to devices for transmitting motion between two coaxial rotating shafts of the type adapted to produce a high motion reducing ratio. For convenience, such devices will hereinafter be referred to as "motion reducing devices."
There are several known motion reducing devices of the type which employ an intermediate disk secured to the driven shaft. This disk has an annular toothed portion engageable in a limited sector with an annular toothed portion of a stationary rigid disk, the teeth of the latter being pitched slightly differently from those of the flexible disk. The engaging sector is continuously changed by action of a member rotating with the driving shaft.
For example, in a motion reducing device for a vehicle window regulator, known from U.S. Pat. No. 3,525,890, the engaging sector of a wobble gear is defined by a plurality of balls rolling in a cam shaped groove of a member rotatable with the rotor of a flat electric motor. The output shaft is sealed with respect to a rigid disk which seals the motor armature, thus preventing adverse affect on the electric motor and the device from exposure to ambient atmosphere. This device has the disadvantage of providing poor torque, due to the flat motor, and of being expensive to manufacture, due to the cam groove and the plurality of balls.
U.S. Pat. No. 3,796,898 discloses a motion reducing device for mechanisms dangerous or not readily accessible including a stationary toothed disk and a flexible toothed disk, the latter secured to the driven shaft. The flexible disk is deformed by a roller carried by a member secured to the motor shaft. However, the device is not protected by any closed structure and cannot be properly lubricated.
Another motion reducing device is known from U.S.S.R. certificate No. 684,226 wherein a wobble gear is engaged by a pair of intermediate friction rings which are carried by an eccentric wave generator and engage two oppositely inclined surfaces of a stationary ring. The joint action of the eccentric motion and the inclined surfaces of the stationary ring causes the intermediate rings to wobble oppositely around the common axis of the two shafts. The wobble disk and the rings are carried by a cylindrical box rotatably mounting the two shafts by means of revolving bearings. This device has the disadvantages of producing high friction between the rings and the inclined surfaces while at the same time making no provision for seals between the box and the two shafts.